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Thursday, January 31, 2008

Extraocular Muscle Movements - Function Explained

Usually, anatomists and clinicians share the same base of knowledge regarding how the body functions. However, as I was doing Step I practice questions today, I came across a question that referred to the functions of the extra-ocular muscles. As I flipped through First Aid for the USMLE Step 1, I noticed that the section on extra-ocular muscles had been visited by me before:

Abduction:Inferior obliqueSuperior rectusInferior oblique
...

Apparently, I had reviewed this topic at various times and found varying results from different sources. I decided to end this once and for all with the med student's almost authoritative resource: Wikipedia. The page that came up was helpful, but Wikipedia posed more questions than it answered. Apparently, clinicians in the past believed that the obliques adducted, while anatomists begged to differ. Luckily, a reference to a British Medical Journal article resolved the issue: the anatomists won, the obliques abduct.

It is interesting to see how someone's mistake if inculcated enough can become dogma. Simply by looking at the muscles, as was pointed out to me, the actions are apparent. As the obliques attach on the temporal aspect of the orbit, when they contract, the orbit will rotate against the force around its axis. In other words, the eye will abduct. How clinicians missed this for apparently a long time is beyond me. However, the British have a theory:

Our final conclusions, and what is now our policy for instruction on this muscle, is as follows. The superior oblique, actingin isolation, turns the eye down and out. However, if it was testedclinically by the patient being asked to look down and out, itsaction could be mimicked by the combined action of inferior andlateral recti. This is particularly so as the inferior rectusacts most effectively when the eye is abducted (looking laterally).Thus if the patient is asked to look down and in, these musclesare excluded and the problem is solved. Essentially we are testingthe ability of the superior oblique to lookdownwards.
The confusion, which I hope the above clarifies, is compounded by some ophthalmologists being so used to testing the muscleby asking the patient to look down and in that they have forgottenthat the isolated action is down andout.

Ah ha! So it was the ophthalmologists' fault! Well, well. Mystery solved!

1 comment:

haha!!that was nice!hey i'm a medical student and i found this page,while i was searching for info about extraocular muscles for my confrence!and let me tell u the info was helpful,thnx alot!its funny why some people dont see the obvious things?!its my email:longjohnsilver1001@yahoo.com